(1) Field of the Invention
The present invention relates to a method of adjusting a printing position which is adaptable to a printing apparatus having, for example, a monochrome printing head and a color printing head and arranged to perform a printing operation in such a manner that the both printing heads are moved in the direction in which the both printing heads are disposed, a printing apparatus using the adjustment method and a computer readable medium on which a control program of computer readable instructions for performing the adjustment method is stored.
(2) Description of the Related Art
Due to the advent of powerful personal computers, graphics-intensive processes can now be relatively easily performed. Accordingly, there has arisen a requirement for a printing apparatus capable of producing high-quality color graphical output on hard copy. To satisfy the above-mentioned requirement, printing apparatuses of a type having an ink jet printing head have been provided. The ink jet printing apparatuses of the foregoing type are able to perform a printing operation with a relatively low noise sound level. Moreover, the ink jet printing apparatuses are able to form a small dot at a high density. Therefore, the ink jet printing apparatuses of the foregoing type have been employed to perform a multiplicity of printing operations including color printing.
The ink jet printing apparatus of the foregoing type incorporates an ink jet printing head arranged to be supplied with ink from an ink accommodating means and a paper feeding means for relatively moving recording paper with respect to the ink jet printing head. In response to a print command signal, an ink droplet is discharged to form a dot so that a printing operation is performed.
The printing apparatus of the foregoing type has a common head holder (carriage) on which a monochrome printing head, capable of discharging black ink, and a color printing head, capable of discharging a plurality of colored inks (e.g., yellow, cyan, and magenta ink), are mounted. Thus, the printing apparatus of the foregoing type is able to perform a full color printing operation, by changing the discharge ratio of ink in the foregoing colors, and also is able to print text using black ink.
The carriage on which the monochrome printing head and the color printing head are mounted is pulled by a timing belt which is rotated by a motor for operating the carriage so as to perform a reciprocating motion in the direction of the printing lines. That is, both of the monochrome printing head and the color printing head are moved in the direction in which the two heads align so that the printing operation is performed.
In the above-mentioned printing apparatus, the monochrome printing head is spaced from the color printing head. In other words, they are disposed apart from each other. Because the two printing heads are spaced from each other, it is impossible to print in the same location from both heads at the exact same time. Therefore, when ink is to be discharged from the two printing heads in the same location, a precise alignment between the two heads is necessary. In particular, the monochrome printhead will print in a particular location at a timing different from when the color printhead prints at that same location. In other words, printing cannot be performed at the same position of paper at the same timing. Therefore, ink discharge is performed in such a manner that timings of print signals arranged to be supplied to the two heads are shifted from each other. Thus, the printing position (the ink arrival position) of the monochrome printing head and the printing position of the color printing head are adjusted to coincide with each other in the direction in which the heads are moved.
However, variations of the two assembled heads, change in the environmental temperature and vibrations cause the relative positions between the two heads to be deviated. As a result, the printing position of the monochrome printing head and that of the color printing head are deviated from each other in the direction in which the two heads are moved. As a result, the quality of the printed image deteriorates.
To modify deviation in the printing position, a printing apparatus having a function capable of adjusting the printing position has been provided. FIG. 4 shows a method of adjusting the printing position employed by a printing apparatus having the conventional function of adjusting the printing position. The printing-position adjustment method is arranged in such a manner that timing data for delaying timing stored in a control unit of the printing apparatus is gradually changed. Thus, a plurality of stepped-deviation patterns (in this case, twelve patterns (A) to (L)) in which the quantity of relative deviation in the printing timing between the monochrome printing head and the color printing head is changed in a stepped manner are simultaneously printed on one page of A4-size paper.
In the pattern shown in FIG. 4, solid lines indicate results of printing operations performed by the monochrome printing head and dashed lines indicate results of printing operations performed by the color printing head. When the ink jet printing apparatus prints the foregoing patterns, upper half nozzles of nozzle lines on the ink discharge surface of the printing head composed of a plurality of nozzles of the monochrome head disposed in a direction perpendicular to the direction (the main scanning direction) in which the heads are disposed are used. On the other hand, lower half nozzles of the color head are used by the color head.
As can be understood from the patterns (A) to (L), the printing positions (indicated by the dashed lines) of the color head with respect to the printing positions (indicated by the solid lines) of the monochrome head are, in a stepped manner, deviated in a rightward direction from the pattern (A) to the pattern (L). That is to say, each of the patterns is printed with a different respective print deviation timing value. This timing value varies in a stepped manner from one to another of the printed patterns. The steps are all the same, and the difference between one pattern and the next may be understood to be a step size.
A user subjects the patterns (A) to (L) to comparisons to select a pattern having the smallest quantity of deviation. Then, a symbol corresponding to the selected pattern is input to the printing apparatus. Since the pattern (I) has the smallest quantity of deviation in this case, symbol (I) is input to the printing apparatus.
When the symbol corresponding to the pattern is input to the printing apparatus, data corresponding to the symbol (which is I in this case), is written on a control unit of the printing apparatus (hereinafter also called as a "printer") so that adjustment of the printing position is completed.
When the printing position is adjusted, color of ink for use to print the pattern by the color printing head is limited to a specific color (for example, cyan).
The above-mentioned conventional method of adjusting the printing position of the printing apparatus is arranged in such a manner that a plurality of patterns are printed one time and an optimum pattern among the plural patterns is selected by a user. Therefore, if the range of the quantity of deviation which can be adjusted is enlarged or if the adjustment accuracy is improved (that is, if the quantity of change (the quantity of deviation) between patterns is reduced), there arises a problem in that an operation required for the user to perform selection becomes too complicated.
The foregoing fact will specifically be described. In general, the quantity of change which can be determined visually by a human being is limited to 0.01 mm. If the quantity of change between patterns in the stepped manner is too large (i.e., if the step size is too large), a required adjustment cannot be performed. If the quantity of change is determined to be 0.1 mm and the number of patterns which can be printed on A4-size paper is assumed to be 15, the quantity of deviation which can be adjusted by the conventional printing-position adjustment method for the printing apparatus is 1.4 mm (the value is not 15 mm because of existence of a central value).
However, the deviation of the printing position between the two heads occurring due to the foregoing change in the environmental temperature or the like is sometimes 1.4 mm or greater. When the range in which the printing position can be adjusted is enlarged to, for example, about 2.9 mm to overcome the above-mentioned problem, the conventional method of adjusting the printing position is required to simultaneously print thirty patterns.
Since the above-mentioned patterns cannot be printed on one A4-size paper, the patterns are printed across a page boundary. Therefore, the user must subject the thirty patterns printed across the page boundary to comparisons to select one optimum pattern. Therefore, there arises a problem in that a complicated adjustment operation must be performed.
Today, printing apparatuses are now able to form images with higher resolution than ever before. With such high-resolution printing, even a slight deviation in the printing position of the monochrome printing head vis-a-vis the printing position of the color printing head produces a very noticeable decrease in image printing quality. To put it another way, in high-quality printing, there is an excessive influence on print quality when there is even a slight deviation in the printing position between the monochrome printing head and the color printing head. Therefore, the process of adjusting the alignment of the two printheads with each other must be more precise than ever. That is, improvement in the adjustment accuracy (reduction of the quantity of change (the quantity of deviation) between patterns in the stepped manner) has been required.
If the quantity of change is set to be 0.05 mm and the quantity of deviation which can be adjusted is made to be 1.4 mm (which is not 2.9 mm) to satisfy the above-mentioned requirement, the conventional printing-position adjustment method is required to print thirty patterns. Therefore, the thirty patterns are printed across the page boundary of A4-size paper.
Similarly, the user must subject the thirty patterns printed across the page boundary to comparisons to select one optimum pattern. Therefore, there arises the same problem in that a complicated adjustment operation must be performed. Also in this case, a multiplicity of patterns of small quantities of change must simultaneously be subjected to comparisons. Providing the user with such a great number of different printed patterns, each varying from the other by such very small quantities of change, makes the adjustment operation much too complicated complicated for average users to perform.
As described above, the conventional printing-position adjustment method is arranged in such a manner that a plurality of patterns are printed one time to cause a user to select one optimum pattern. Therefore, if the range of the quantity of deviation which can be adjusted is enlarged or if the adjustment accuracy is improved, the user cannot smoothly perform the selecting operation.
The conventional printing-position adjustment method has the structure that the color for use to print the patterns by the color printing head is limited to a specific color. Therefore, only the ink of the specific color is consumed in a larger quantity as compared with ink of the other colors. If cyan ink is used to print the patterns by the color ink jet printing head, only the cyan ink is consumed in a larger quantity as compared with ink of the other colors.
In general, an ink pack in which yellow, cyan and magenta ink is enclosed is mounted on a cartridge of color ink. If ink of a certain color is somewhat consumed, the cartridge must be changed.
That is to say, an ink pack that has three colors such as yellow, cyan, and magenta, must have some of each color ink to print. If the ink of one specific color is deemed to be at a level that is too low, it is necessary to change the entire cartridge even though there is plenty of the other colors of ink remaining in the cartridge. Discarding a cartridge that is only low in one color of ink is uneconomical and wasteful, and causes a problem for users.